examples: add unit testing example

examples/system/unit_test/main/example_unit_test_main.c

@@ -0,0 +1,40 @@
+/* Example application which uses testable component.
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#include <stdio.h>
+#include "esp_system.h"
+#include "testable.h"
+
+/* This application has a test subproject in 'test' directory, all the
+ * interesting things happen there. See ../test/main/example_idf_test_runner_test.c
+ * and the makefiles in ../test/ directory.
+ *
+ * This specific app_main function is provided only to illustrate the layout
+ * of a project.
+ */
+
+void app_main(void)
+{
+    const int count = 32;
+    const int max = 100;
+
+    printf("In main application. Collecting %d random numbers from 1 to %d:\n", count, max);
+    int *numbers = calloc(count, sizeof(numbers[0]));
+    for (int i = 0; i < count; ++i) {
+        numbers[i] = 1 + esp_random() % (max - 1);
+        printf("%4d ", numbers[i]);
+        if ((i + 1) % 10 == 0) {
+            printf("\n");
+        }
+    }
+
+    int mean = testable_mean(numbers, count);
+    printf("\nMean: %d\n", mean);
+    free(numbers);
+}